Optical sensing and control of ultraviolet fluid treatment dynamics

ABSTRACT

An ultra violet light sterilizing apparatus includes in one embodiment a fluid chamber, at least one ultraviolet light source configured to emit ultraviolet light into the fluid chamber, and at least one ultraviolet light sensor that includes a photodiode. The photodiode is a silicon carbide photodiode, a gallium nitride photodiode, or an aluminum gallium nitride photodiode. Each UV light sensor includes a sealed outer housing having an optically transparent window. The photodiode is located inside the housing adjacent the transparent window. Each UV light sensor also includes a signal amplification unit that includes an amplifier mounted on a printed circuit board located inside the housing. The UV sterilization apparatus also includes a controller configured to receive, as input, a signal from each ultraviolet light sensor. The controller compares the input signal to a desired UV light intensity and outputs a control signal to each ultraviolet light source to adjust the intensity of the ultraviolet light emitted from each ultraviolet light source.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/259,405 filed Feb. 26, 1999 now U.S. Pat. No. 6,057,917.

BACKGROUND OF THE INVENTION

This invention relates generally to ultraviolet light treatment offluids and more particularly, to optical sensing and control ofultraviolet light intensity levels in an ultraviolet light fluidtreatment process with photodiode detectors.

Ultraviolet (UV) light may be used to sterilize water and other fluids.The ultraviolet light disrupts the DNA of microorganisms in the fluid,which prevents reproduction and thus kills the microorganisms.Regulation of UV light intensity is important in the UV lightsterilization process because a minimum level of ultraviolet lightintensity is typically required. Also, excessive levels of UV lightintensity can result in high maintenance and an associated higheroperation cost.

Photodiodes are sometimes used to detect and regulate UV light intensityin such sterilization processes. The UV light spectrum includeswavelengths from 10 to 400 nanometers (nm). However, typical photodiodesused to measure UV light in the known UV light sterilization processesare usually broad range wavelength detectors. For example, silicondetectors are used which are sensitive to light wavelengths ranging from200 to 1100 nm. Gallium arsenide phosphide and gallium phosphidedetectors, which are sensitive to light wavelengths ranging from 200 to650 nm, are also used. These devices are inherently sensitive to visibleand infrared light waves in addition to the UV spectrum. When only UVlight detection is desired and outside light sources such as visiblelight are also present, erroneous signals may result.

Therefore, filters are needed to block out wavelengths longer than 400nm to eliminate erroneous signals triggered by other light sources.However, filters are prone to degradation which can lead to permittinglight out side the UV spectrum into the detector, which results in falseand inaccurate readings. Additionally, filter degradation results incostly maintenance and/or equipment downtime.

It would be desirable to provide an ultraviolet light sterilizationprocess incorporating a UV detector that is not sensitive to lightoutside the UV spectrum to eliminate erroneous signals caused by ambientlight sources. It would further be desirable to provide an ultravioletlight sterilization process that does not depend upon light filtersthereby lowering g maintenance costs and equipment downtime due tofilter repair or replacement.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment, an ultra violet light sterilizing apparatusutilizing a photodiode sensor includes a silicon carbide (SiC)photodiode, a gallium nitride (GaN) photodiode, or an aluminum galliumnitride (AlGaN) photodiode. The ultraviolet light fluid sterilizationapparatus includes a fluid chamber, at least one ultraviolet lightsource configured to emit ultraviolet light into the fluid chamber, andat least one ultraviolet light sensor that includes a photodiode.

Each UV light sensor includes a sealed outer housing having an opticallytransparent window. A silicon carbide photodiode, a gallium nitridephotodiode, or an aluminum gallium nitride photodiode is located insidethe housing adjacent the transparent window. The housing also includesat least one sealable outlet to permit electrical wire connections topass into the housing. The optically transparent window may befabricated from sapphire or quartz.

The UV light fluid sterilization a pparatus further includes acontroller for sampling the signal from each ultraviolet light sensor.The controller compares the sampled signals to a desired UV lightintensity and outputs a control signal to each ultraviolet light sourceto adjust the intensity of the ultraviolet light emitted from eachultraviolet light source.

In operation, fluid flows into the chamber of the ultraviolet lightsterilization apparatus. The fluid is then irradiated with UV light fromthe ultraviolet light source. The UV light sensor measures the intensityof the UV light inside the chamber of the apparatus and the controllersamples the signal generated by the sensor. Particularly, the photodiodesenses the intensity of the UV light inside the chamber, the signalamplification unit amplifies the signal, and the controller samples thesignal generated by the sensor. The controller ascertains any differencebetween the sensed UV intensity and a predetermined desired UVintensity. The controller then adjusts the intensity of the ultravioletlight source to correspond to the predetermined level of UV intensity.

The above described ultraviolet light fluid sterilization apparatusutilizes a UV detector that is not sensitive to light outside the UVspectrum and thus eliminates erroneous signals caused by ambient lightsources. Particularly, the UV sensor has good UV sensitivity in the 200to 300 nm band and is insensitive to infrared radiation above 400 nm.Also because the UV sensor is not sensitive to light having wavelengthsgreater than 400 nm, light filters are not required to filter ambientlight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an ultraviolet light fluid sterilizationapparatus in accordance with one embodiment of the present invention.

FIG. 2 is a sectional side view of the ultraviolet light sensor shown inFIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of an ultraviolet light fluid sterilizationapparatus 10 in accordance with an embodiment of the present invention.Apparatus 10 sterilizes or disinfects various fluids, for example,water, by delivering concentrated doses of ultraviolet energy to thefluid. The ultraviolet energy, also called UV light, disrupts the DNA ofmicroorganisms in the fluid preventing reproduction and thus killing themicroorganisms. Of course, apparatus 10 is suitable for sterilizingother fluids besides water, for example, compressed air, oils, blood,and other body fluids. To successfully sterilize a fluid, a minimumlevel of ultraviolet light intensity is required. Apparatus 10 includesan ultraviolet light sensor 12 to measure UV light intensity and acontroller 14 to ascertain any difference between the sensed UVintensity and a predetermined desired intensity and to adjust the outputof an ultraviolet light source 16 to achieve the desired level of UVlight intensity.

Apparatus 10 also includes a chamber 18 having an inlet 20 and an outlet22. Chamber 18 is a tube through which the fluid may continuously flow.Alternatively, chamber 18 may be a tank which permits a longer dwelltime of the fluid in chamber 18. A tank permits batch processing of thefluid, while a tube generally is used for continuous processing of thefluid as it flows through chamber 18.

UV light source 16 is located inside chamber 18. However, UV lightsource 16 may be located outside chamber 18 adjacent an opening orwindow in chamber 18 that permits the UV light emitted from light source16 to enter chamber 18.

UV light sensor 12 is mounted on a wall 24 of chamber 18. Particularly,sensor 12 extends through an opening 26 in wall 24 so that at least aportion of sensor 12 is located inside chamber 18. However in analternative embodiment, UV light sensor 12 may be mounted outsidechamber 18 adjacent an opening or window permitting UV light to passfrom inside chamber 18 to sensor 12.

UV light sensor 12 and UV light source 16 are each electricallyconnected to controller 14. Particularly, sensor 12 is coupled tocontroller 14 by a controller input line 28. UV light source 16 iscoupled to controller 14 by a controller output line 30.

FIG. 2 is a sectional side view of ultraviolet light sensor 12. UVsensor 12 includes a sealed housing 32. An optically transparent window34 is located in a first end 35 of housing 32. Optically transparentwindow 34 permits UV light to enter housing 32. Window 34 may befabricated from any suitable material, for example sapphire or quartz. Aphotodiode 36 is located inside housing 34 adjacent to window 34.Photodiode 36 is a silicon carbide photodiode, a gallium nitridephotodiode, or an aluminum gallium nitride photodiode. A SiC photodiode36 is sensitive to light of about 200 to about 400 nm wavelength whichis within the UV spectrum of about 10 to 400 nm. A SiC Photodiode 36 isnot sensitive to infrared and visible light having wavelengths greaterthan 400 nm.

A GaN photodiode 36 is sensitive to light of about 190 to 365 nm. With aGaN photodiode 36, sensor 12 sensitivity peaks at approximately thelimit of 365 nm and then experiences an abrupt cut-off in sensitivity.This feature enhances the functionality of UV sensor 12 in that anylight above 365 nm wavelength is ignored.

Adding aluminum to the gallium nitride substrate to form an AlGaNphotodiode 36 permits a shift in the cut-off wavelength of the GaNphotodiode depending on the mole composition of aluminum and gallium inthe photodiode. Particularly, for a photodiode fabricated from amaterial having the formula Al_(X)Ga_(1−X)N, where X is defined as amole composition having a value from 0 to 1, the cut-off wavelengthdepends on the value of X. For example, with a value of X=1, theresulting photodiode is an AlN photodiode with a cut-off wavelength of200 nm. With a value of X=0, the resulting photodiode is a GaNphotodiode with a cut-off wavelength of 365 nm. With a value of Xbetween 0 and 1, the resulting photodiode is an AlGaN photodiode havinga cut-off wavelength between 200 and 365 nm depending on the value of X.Specifically, as the value of X approaches 0, the cut-off wavelength ofthe photodiode approaches 365 nm.

Because photodiode 36 is not sensitive to light outside the UV spectrum,stray ambient light entering chamber 18 (shown in FIG. 1) will not causeerroneous readings by sensor 12 of the UV light intensity inside chamber18. A TEFLON® (polytetrafluoroethylene) plastic insert 38, configured tofit inside first end 35 of housing 32 and engage wall 39 of housing 32,holds photodiode 36 in place adjacent window 34.

Sensor 12 also includes a signal amplification unit 40 electricallyconnected to photodiode 36 by conductors 42. Signal amplification unit40 includes a signal amplifier 44 mounted on a printed circuit board 46.Circuit board 46 is mounted inside housing 32. Conductors 42 areelectrically connected to signal amplifier 44 through printed circuitboard 46. Controller input line 28 enters housing 32 through a sealableinlet 48. Controller input line 28 is electrically connected to signalamplifier 44 through printed circuit board 46. In an alternateembodiment, signal amplification unit 40 is located outside and separatefrom housing 32.

In operation, fluid flows into chamber 18 of ultraviolet lightsterilization apparatus 10. The fluid is then irradiated with UV lightfrom ultraviolet light source 16. UV light sensor 12 is responsive tothe intensity of the UV light inside chamber 18. Particularly,photodiode 36 generates a signal representative of the intensity of theUV light inside chamber 18. The generated signal is amplified by signalamplifier 44 of signal amplification unit 40, and controller 14 samplesthe amplified signal on input line 28. Controller 14 ascertains anydifference between the sensed UV intensity and a predetermined desiredUV intensity. Controller 14 then sends a control signal throughcontroller output line 30 to adjust the intensity of ultraviolet lightsource 16 to correspond to the predetermined UV intensity level. Forexample, if the sensed UV intensity inside chamber 18 is below thedesired UV intensity, controller 14 causes UV light source 16 toincrease UV light output.

The above described ultraviolet light fluid sterilization apparatus 10utilizes UV sensor 12 that is not sensitive to light outside the UVspectrum. Because sensor 12 is not sensitive to light outside the UVspectrum, there are no erroneous signals from sensor 12 caused byambient light sources. Erroneous signals from sensor 12 could causecontroller 14 to adjust the UV intensity too low for propersterilization. By elimination of erroneous UV intensity signals,photodiode sensor 12 ensures that UV light sterilization apparatus 10operates efficiently to produce safe sterilized fluids. Additionally,varying mole compositions of aluminum and gallium in an AlGaN photodiodecan change the cut-off wavelength to a specific wavelength which permitscustomizing sensor 12 for an intended application. Further, becausephotodiode sensor 12 is not sensitive to light outside the UV spectrum,the use of light filters to eliminate ambient light is not required.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

What is claimed is:
 1. An ultraviolet light sensor device for a fluidsterilizing apparatus including a UV light source, said sensor devicecomprising: an ultraviolet light sensitive photodiode, said photodiodecapable of generating a signal proportional to the intensity ofultraviolet light generated by the UV light source and detected by saidphotodiode, said photodiode comprised of a material having the formulaAl_(X)Ga_(1−X)N, where X has a value from 0 to 1; and a sealed outerhousing comprising an optically transparent window, said photodiodelocated inside said housing and adjacent said transparent window.
 2. Anultraviolet light sensor device in accordance with claim 1 furthercomprising a signal amplification unit coupled to said photodiode.
 3. Anultraviolet light sensor device in accordance with claim 2 wherein saidsignal amplification unit comprises an amplifier mounted on a printedcircuit board, said printed circuit board located inside said housing.4. An ultraviolet light sensor device in accordance with claim 1 whereinsaid photodiode is sensitive to light having a wavelength ranging fromabout 190 to about 365 nanometers.
 5. An ultraviolet light sensor devicein accordance with claim 1 wherein said optically transparent windowcomprises sapphire or quartz.
 6. An ultraviolet light sensor device inaccordance with claim 1 wherein said housing further comprises at leastone sealable outlet to permit electrical wire connections to passthrough said housing.
 7. An ultraviolet light fluid sterilizationapparatus comprising: a fluid chamber: at least one ultraviolet lightsource configured to emit ultraviolet light into said fluid chamber; andat least one ultraviolet light sensor comprising a photodiode, saidphotodiode comprised of a material having the formula Al_(X)Ga_(1−X)N,where X has a value from 0 to 1, said photodiode configured to generatea signal proportional to the intensity of ultraviolet light generated bysaid UV light source and detected by said photodiode.
 8. An apparatus inaccordance with claim 7 wherein said ultraviolet light sensor furthercomprises: a sealed outer housing comprising an optically transparentwindow, said photodiode located inside said housing and adjacent saidtransparent window; and a signal amplification unit coupled to saidphotodiode.
 9. An apparatus in accordance with claim 8 wherein saidsignal amplification unit comprises an amplifier.
 10. An apparatus inaccordance with claim 9 wherein said amplifier is mounted on a printedcircuit board, said printed circuit board located inside said housing.11. An apparatus in accordance with claim 7 wherein said photodiode issensitive to light having a wavelength ranging from about 190 to about365 nanometers.
 12. An apparatus in accordance with claim 7 wherein saidoptically transparent window comprises sapphire or quartz.
 13. Anapparatus in accordance with claim 7 wherein said housing furthercomprises at least one sealable outlet to permit electrical wireconnections to pass through said housing.
 14. An apparatus in accordancewith claim 13 further comprising a controller configured to receive, asinput, a signal from said ultraviolet light sensor and to output acontrol signal to said ultraviolet light source to control the intensityof the ultraviolet light emitted from said ultraviolet light source. 15.A method of sterilizing a fluid utilizing an ultraviolet light fluidsterilization apparatus, the sterilization apparatus comprising a fluidchamber, at least one ultraviolet light source, and at least oneultraviolet light sensor, each ultraviolet light source configured toemit ultraviolet light into the fluid chamber, and each ultravioletlight sensor comprising a photodiode, the photodiode comprised of amaterial having the formula Al_(X)Ga_(1−X)N, where X has a value from 0to 1 and configured to generate a signal proportional to the intensityof ultraviolet light generated by the UV light source and detected bythe photodiode, said method comprising the steps of: flowing a fluidinto the chamber of the ultraviolet light sterilization apparatus;irradiating the fluid with ultraviolet light from the at least oneultraviolet light source of the sterilization apparatus; sampling asignal generated by the ultraviolet light sensor with the controller;and adjusting the level of ultraviolet light intensity in the chamberbased on the sampled signal and with an output signal from thecontroller to the light source.
 16. A method in accordance with claim 15wherein each ultraviolet light sensor further comprises: a sealed outerhousing comprising an optically transparent window, the photodiodelocated inside the housing and adjacent the transparent window; and asignal amplification unit.
 17. A method in accordance with claim 16wherein signal amplification unit comprises an amplifier mounted on aprinted circuit board, the printed circuit board located inside thehousing.
 18. A method in accordance with claim 16 wherein the photodiodeis sensitive to light having a wavelength ranging from about 190 toabout 365 nanometers.
 19. A method in accordance with claim 16 whereinthe optically transparent window comprises sapphire or quartz.
 20. Amethod in accordance with claim 16 wherein said housing furthercomprises at least one sealable outlet to permit electrical wireconnections to pass through said housing.